The subject invention is directed toward the valve art and, more particularly, to a metering valve having improved stability.
The invention is particularly suited for use in a needle type metering valve of the type used for controlling fine flows and will be described with particular reference thereto. However, as will become apparent, the inventive concept presented is capable of broader applications and use.
Valves used for metering fine flows typically comprise a needle member or metering pin carried at the end of a stem and adapted to enter a fluid flow orifice in a valve body between the fluid inlet and outlet. Generally, the stem is threadedly received in a multi-part bonnet member which, in turn, is threadedly secured to the body. Rotation of an associated handle imparts axial movement of the stem and needle member, and regulates fluid flow through the valve. An O-ring or the like is carried on the stem and assists a conventional stem packing for sealing purposes.
In recent years, a quality control study has determined that metering valves of this general type have been failing prematurely due to breakage and galling of the metering pin. It is desirable to extend the cycle life of the metering valves and retain high quality metering after repetitive use. A review of the valve designs found that improvements were obtainable in certain areas, e.g., better alignment of the metering pin in relation to the orifice, reduction of tolerance stacking, better force absorption, and the like. The variation in concentricity and tolerance stacking allowed the metering pin to rub the orifice side wall. This caused the metering pins to break or gall since the resulting forces could not be absorbed by the stem and bonnet assemblies.
Flow instability problems also reulted at low pressure ranges. Variations in flow were not uncommon upon imposition of slight lateral loads on the handle. These flow variations are particularly undesirable when handling toxic or corrosive fluids where a highly accurate, precise flow is required.
A valve arrangement has, therefore, been considered desirable which would provide improved valve life and overcome the foregoing problems. The subject invention is deemed to meet these needs and others, and provides a new and improved metering valve construction.